JP2006173365A - Irradiating light quantity measuring instrument and euv exposing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an irradiating light quantity measuring instrument that can accurately measure the quantity of EUV light irradiated upon a surface to be irradiated even if contamination easily adheres to the surface irradiated by EUV. <P>SOLUTION: On the surface of a mirror substrate 1, a multilayered film 2 is formed to cover the effective area 4 of a mirror. Since an ammeter A1 is electrically connected to the multilayered film 2, the photoelectronic current discharged when the EUV light is made incident can be measured. The EUV light made incident to the mirror is made incident to an EUV light incident range 5 which is slightly wider than the effective area 4. In the EUV light incident range 5, a photoelectron detecting thin film 3 is formed outside the effective area 4. Since another ammeter A2 is electrically connected to the thin film 3, the photoelectronic current discharged when the EUV light is made incident can be measured. Since the ammeters A1 and A2 are used for measuring the photoelectronic currents, the irradiated quantity of the EUV light can be measured accurately by compensating the influence of adhered contamination. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is an EUV exposure apparatus (also referred to as an extreme ultraviolet exposure apparatus, and in the present specification and claims, refers to an exposure apparatus using ultraviolet light having a wavelength of 10 to 15 nm). The present invention relates to an irradiation light amount measuring device for measuring the amount of irradiation light on a surface, and an EUV exposure apparatus having the irradiation light amount measuring device.

  In recent years, with the miniaturization of semiconductor integrated circuits, EUV light having a shorter wavelength (10 to 15 nm) is used in place of conventional ultraviolet rays in order to improve the resolving power of an optical system limited by the diffraction limit of light. Projection lithography techniques have been developed (see, for example, D. Tichenor, et al, SPIE 2437 (1995) 292: Non-Patent Document 1). This technique is recently called EUV (Extreme UltraViolet) lithography, and is expected as a technique capable of obtaining a resolution of 70 nm or less, which cannot be realized by conventional optical lithography using light having a wavelength of about 190 nm.

  A complex refractive index n of a substance in a wavelength region of EUV light is represented by n = 1−δ−ik (i is a complex symbol). The imaginary part k of the refractive index represents absorption of extreme ultraviolet rays. Since δ is much smaller than 1, the real part of the refractive index in this region is very close to 1. Moreover, since k is very large, the absorption rate is large. Accordingly, a transmission / refraction type optical element such as a conventional lens cannot be used, and an optical system utilizing reflection is used.

  An outline of the EUV exposure apparatus is shown in FIG. The EUV light 32 emitted from the EUV light source 31 enters the illumination optical system 33, becomes a substantially parallel light beam via a concave mirror 34 that acts as a collimator mirror, and enters an optical integrator 35 including a pair of fly-eye mirrors 35a and 35b. Incident. As the pair of fly-eye mirrors 35a and 35b, for example, a fly-eye mirror disclosed in JP-A-11-312638 (Patent Document 1) can be used. In addition, since the more detailed structure and effect | action of a fly eye mirror are demonstrated in detail in patent document 1, and since there is no direct relationship with this invention, the description is abbreviate | omitted.

  Thus, a substantial surface light source having a predetermined shape is formed in the vicinity of the reflecting surface of the second fly's eye mirror 35b, that is, in the vicinity of the exit surface of the optical integrator 35. The light from the substantial surface light source is deflected by the plane mirror 36 and then forms an elongated arc-shaped illumination area on the mask M (the aperture plate for forming the arc-shaped illumination area is not shown). ing). The light from the illuminated pattern of the mask M forms an image of the mask pattern on the wafer W via the projection optical system PL composed of a plurality of mirrors (six examples of mirrors M1 to M6 in FIG. 5). .

  An optical system using such a mirror cannot use paraxial rays for projection exposure, and therefore has a ring-shaped projection exposure field in order to correct the entire aberration as uniform. . In such a ring-shaped projection exposure field, chips of about 30 mm square cannot be exposed at a time, so that exposure is performed by synchronously scanning the mask and wafer.

  In such an EUV exposure apparatus, the irradiation light amount of the EUV light that illuminates the mask M surface in a predetermined exposure state and the irradiation light amount of the EUV light that irradiates the wafer W surface are known, and the state of the EUV light source 31 is adjusted accordingly. May be necessary.

  For this purpose, when the mask M is in the retracted state or when the wafer W is not placed on the wafer stage, for example, a sensor made of a photoelectric element is placed on the mask M or the wafer W during exposure. A method is considered in which the amount of irradiation light is detected from the output of the sensor in the position.

  However, this method has a problem that it is impossible to know the amount of irradiation light at the time of actual exposure. Therefore, it is considered to detect the amount of photoelectrons received by the reflective film of the mirror of the EUV exposure apparatus during actual exposure and indirectly detect the amount of light received by the mask M and the wafer W from the value.

  Usually, as these mirrors, multilayer mirrors in which thin films made of Mo and Si are alternately formed on a glass substrate are used. Current flowing between the multilayer film and the ground potential (photocurrent) ) Is measured, the amount of EUV light irradiated onto the mirror can be known, and from this, the amount of EUV light irradiated onto the mask M and wafer W can be indirectly determined.

JP 11-312638 A D. Tichenor, et al, SPIE 2437 (1995) 292

  However, in the EUV exposure apparatus, the problem that the mirror surface is contaminated by contamination is unavoidable. In these EUV exposure apparatuses, the mirror is used in a vacuum to prevent absorption by air. However, the inside of the exposure apparatus is not completely evacuated and is in an environment where organic gases such as hydrocarbons are always present. Residual gases containing hydrocarbons include those caused by oil used in the vacuum exhaust system (vacuum pump), those caused by lubricants in moving parts inside the equipment, and parts used inside the equipment (for example, electric cables) Due to the coating material).

  In the case of an EUV exposure apparatus, a wafer coated with a photoresist is introduced into a vacuum inside the apparatus. When irradiated with EUV light, hydrocarbon-containing gas is released due to evaporation of the remaining solvent, decomposition and desorption of the resin constituting the resist, and the like.

  Residual gas molecules containing hydrocarbons are physically adsorbed on the surface of the multilayer mirror. Physically adsorbed gas molecules are repeatedly desorbed and adsorbed and do not grow thick as they are.

  However, when EUV light is irradiated here, secondary electrons are generated inside the mirror substrate, and the secondary electrons decompose hydrocarbon molecules adsorbed on the surface to deposit carbon. .

  As the adsorbed gas molecules are decomposed and deposited more and more, a carbon layer is formed on the surface of the multilayer mirror, and its thickness increases in proportion to the irradiation amount of EUV light.

  When contamination such as carbon adheres to the surface of the multilayer mirror, emission of photoelectrons is blocked. Therefore, by measuring only the photocurrent flowing between the multilayer film and the ground potential, it is possible to distinguish whether the change is due to a change in the amount of incident EUV light or due to contamination. As a result, there was a problem that the amount of irradiation light could not be measured accurately.

  The present invention has been made in view of such circumstances, and an EUV light irradiation light amount measuring apparatus capable of accurately measuring the amount of irradiation light even when contamination easily adheres to a surface irradiated with EUV light. It is another object of the present invention to provide an EUV exposure apparatus using the irradiation light amount measuring apparatus.

  A first means for solving the above-described problem is an irradiation light amount measuring apparatus for measuring the irradiation light amount of the EUV light onto the surface to be irradiated, and the photoelectric current generated by the EUV light that irradiates the effective area of the surface to be irradiated And a photoelectron current generated by EUV light incident on a photoelectron detection thin film provided outside the effective area of the irradiated surface, and the amount of irradiation light is measured based on both measured values. It is an irradiation light quantity measuring device (Claim 1).

  Here, the effective area is an area where EUV light that illuminates the area is used for the purpose. In this means, the photoelectron current generated by the EUV light incident on the photoelectron detection thin film provided outside the effective area of the EUV light irradiated surface is measured in addition to the photoelectron current generated by the EUV light irradiating the effective area. ing. Therefore, contamination is different by varying the degree of influence of contamination on the thin film for photoelectron detection provided outside the effective area and the degree of influence of the effective area of the irradiated surface of the EUV light on the surface. The amount of irradiation light can be accurately measured.

  The second means for solving the problem is the first means, and does not block a shielding member that blocks EUV light from a position that blocks irradiation of the EUV light to the photoelectron detection thin film. It is characterized in that it can be moved between positions (Claim 2).

  In this means, when the photocurrent generated in the photoelectron detection thin film provided outside the effective area is not measured, the photoelectron detection thin film is shielded from being irradiated with EUV light by the shielding member. it can. Therefore, the irradiation time of EUV light to the photoelectron detection thin film can be shortened, and contamination can be reduced on the photoelectron detection thin film. Therefore, it is possible to reduce a measurement error caused by adhesion of contamination to the photoelectron detection thin film.

  A third means for solving the above-mentioned problems is the first means or the second means, characterized in that a light cleaning light source for light cleaning the surface of the photoelectron detection thin film is provided. (Claim 3).

  In this means, since the light cleaning light source for optically cleaning the surface of the photoelectron detection thin film is provided, the contamination adhered to the photoelectron detection thin film can be removed by the light cleaning. Therefore, it is possible to reduce a measurement error caused by adhesion of contamination to the photoelectron detection thin film.

  A fourth means for solving the above problem is an irradiation light amount measuring device for measuring the irradiation light amount of the EUV light onto the irradiated surface, and a photoelectron current generated by the EUV light that irradiates the effective area of the irradiated surface. And the photoelectron current generated by the EUV light incident on the photoelectron detection thin film provided so as to be removable from the effective area of the irradiated surface, and the amount of irradiation light is measured based on the measured values of both. An irradiating light amount measuring device (claim 4).

  In the first to third means, the photoelectron detection thin film is provided outside the effective area of the irradiated surface. However, in this means, the photoelectron detection thin film is provided outside the effective area of the irradiated surface. It is provided so that it can be inserted and removed. Therefore, since the photoelectron detection thin film only needs to be inserted outside the effective area of the irradiated surface and measured only when the amount of irradiation light is measured, the adhesion of contamination to the photoelectron detection thin film can be reduced. Therefore, it is possible to reduce a measurement error caused by adhesion of contamination to the photoelectron detection thin film.

  A fifth means for solving the above problem is any one of the first to fourth means, wherein the thin film for photoelectron detection is made of a noble metal (Claim 5). It is.

  Since noble metals hardly adhere to contamination, the use of these as a photoelectron detection thin film can reduce the adhesion of contamination to the photoelectron detection thin film. Therefore, it is possible to reduce a measurement error caused by adhesion of contamination to the photoelectron detection thin film.

  A sixth means for solving the problem is the fifth means, wherein the photoelectron detection thin film made of the noble metal is formed on a glass substrate, the photoelectron detection thin film made of the noble metal and the glass A thin film made of Cr or Ti is formed between the substrate and the substrate (claim 6).

  When a noble metal film is formed on a glass substrate, there is a problem that the noble metal thin film is easily peeled off. However, by interposing a Cr or Ti thin film between the glass substrate and the noble metal thin film, the noble metal thin film can be made difficult to peel off from the glass substrate.

  A seventh means for solving the problem is any one of the first to fourth means, wherein the thin film for photoelectron detection is made of Ni (claim 7). ).

  Since Ni is also difficult to adhere to contamination like noble metals, the use of these as a photoelectron detection thin film can reduce the adhesion of contamination to the photoelectron detection thin film. Therefore, it is possible to reduce a measurement error caused by adhesion of contamination to the photoelectron detection thin film.

  An eighth means for solving the above-mentioned problem is an EUV exposure apparatus (Claim 8) characterized by including the irradiation light amount measuring device of any one of the first to seventh means.

  With this means, the amount of EUV light irradiated on the mask or wafer can be accurately measured during exposure.

  ADVANTAGE OF THE INVENTION According to this invention, even when contamination tends to adhere to the irradiated surface of EUV light, the irradiation light amount measuring apparatus of EUV light which can measure an irradiation light quantity correctly, and this irradiation light amount measuring apparatus are used. An EUV exposure apparatus can be provided.

  Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an outline of an irradiation amount measuring apparatus according to a first embodiment of the present invention, which measures irradiation light applied to a multilayer mirror constituting an EUV exposure apparatus. (A) is a top view, (b) is AA sectional drawing in (a).

  On the surface of the mirror substrate 1 made of low thermal expansion glass, a multilayer film 2 made of alternating layers of molybdenum (Mo) and silicon (Si) for reflecting EUV light having a wavelength of 13.5 nm is formed. The multilayer film 2 is formed so as to cover the effective area 4 of the mirror. An ammeter A1 is electrically connected to the multilayer film 2 so that a photoelectron current emitted when EUV light is incident can be measured.

  The EUV light incident on the mirror is incident on an EUV light incident range 5 that is slightly wider than the effective region 4. Within this EUV light incident range 5, a photoelectron detection thin film 3 is formed in a region outside the effective region 4. An ammeter A2 is electrically connected to the photoelectron detection thin film 3, so that a photoelectron current emitted when EUV light is incident can be measured.

  The thin film 3 for photoelectron detection is formed of a material that is harder to adhere to contamination such as carbon than the multilayer film 2. For example, platinum (Pt) which is a noble metal is used, and chromium (Cr) is first coated on the mirror substrate 1 made of glass, and Pt is coated thereon. Generally, when a noble metal material thin film is formed on glass, it is easy to peel off. However, the adhesion between the mirror substrate 1 and the Pt layer can be improved by inserting a Cr layer. In addition to Pt, gold (Au), rhodium (Rh), palladium (Pd), ruthenium (Ru), or the like may be used as the noble metal. A Ti layer may be provided instead of the Cr layer.

  When this mirror is irradiated with EUV light, the photoelectron current measured by the ammeters A1 and A2 decreases with the irradiation time. The amount of decrease is attributed to both the decrease in the illuminance of the incident EUV light and the effect of preventing the escape of photoelectrons due to contamination such as carbon adhering to the surface.

When the change in illuminance of incident EUV light is ΔE, the initial illuminance of EUV light is E ₀ , the decrease in the amount of photoelectron current due to contamination is ΔC, and the initial value of the photoelectron current is C ₀ , the photoelectron current flowing through the multilayer film 2 Changes in A ₁ and the photoelectron current A ₂ flowing through the photoelectron detection thin film 3 can be expressed as follows. However, the subscripts for ΔC and C ₀ indicate that 1 is for the multilayer film 2 and 2 is for the thin film 3 for photoelectron detection.

If the contamination deposition rate on the surface of the multilayer film 2 and the contamination deposition rate on the surface of the photoelectron detection thin film 3 are measured in advance by experiments, the relative ratio of the decrease in photoelectron current due to contamination deposition can be obtained. This is expressed by the following equation.
ΔC ₁ = nΔC ₂
n is a coefficient representing the ease of adhesion of multilayer film contamination to the photoelectron detection thin film. From these equations, the EUV illuminance drop ΔE / E ₀ and the photoelectron emission drop ΔC ₁ / C ₀₁ and ΔC ₂ / C ₀₂ due to the adhesion of contamination can be calculated separately. That is,

FIG. 2 shows a graph showing changes in the photoelectron current measurement values (A ₁ , A ₂ ) with respect to the EUV light irradiation time. FIG. 2 shows a case in which both A ₁ and A ₂ decrease in the same way with respect to the decrease in illuminance, but the decrease in A ₁ is significant with respect to A ₂ because the amount of contamination is different. According to the above formula, it is possible to separate from these data the decrease in the illuminance of the EUV light and the decrease in the photoelectron current due to the adhesion of contamination.

  As an extreme case, let us consider a case where no contamination adheres on the photoelectron detection thin film 3. In this case, since the coefficient n becomes infinite, the above equations are as follows.

  FIG. 3 is a diagram showing an outline of an irradiation amount measuring apparatus according to the second embodiment of the present invention, which measures irradiation light applied to the multilayer mirror constituting the EUV exposure apparatus. In the following drawings, the same components as those shown in the preceding figures in this column are denoted by the same reference numerals, and the description thereof may be omitted.

  In FIG. 3, the multilayer film mirror is the same as that shown in FIG. 1, the multilayer film 2 is formed on the surface of the mirror substrate 1 made of glass, and outside the effective area within the EUV light incident range, A thin film 3 for photoelectron detection is formed. The photoelectron detection thin film 3 is a Ru thin film. The measurement principle of the irradiation amount of EUV light is the same as that shown in FIG.

  In this embodiment, a movable shielding plate 6 is disposed in the vicinity of the photoelectron detection thin film 3 so that the EUV light 7 is not irradiated on the photoelectron detection thin film 3 except during photocurrent measurement. Yes. Thus, by preventing the EUV light from being irradiated to the photoelectron detection thin film 3 except during measurement, the adhesion of contamination to the photoelectron detection thin film 3 can be reduced, and the sensitivity can be improved over a long period of time. Measurement that does not change is possible.

  FIG. 4 is a diagram showing an outline of an irradiation amount measuring apparatus according to the third embodiment of the present invention, which measures irradiation light applied to a multilayer mirror constituting an EUV exposure apparatus. In this means, the thin film for photoelectron detection is not formed on the surface of the mirror substrate 1, and the member 8 having the Ru film formed as the photoelectric detection surface is inserted in an area outside the effective area of the irradiation area of the EUV light 7. Or withdrawn outside the EUV irradiation area.

  In the state where the member 8 is inserted in the irradiation region of the EUV light 7, the EUV illuminance can be measured by measuring the photocurrent, and the member 8 is moved outside the EUV light irradiation region except during the measurement. In this way, by preventing the EUV light from being irradiated to the Ru film formation region except during measurement, it is possible to prevent contamination from adhering to the Ru region, and to perform measurement without changing the sensitivity over a long period of time. It becomes possible. The position reproducibility of the member 8 on which the Ru film is formed is 10 μm, and can always be inserted at the same position with respect to the EUV light beam.

  Moreover, in the state moved to the EUV non-irradiation region, for example, pulse laser light (KrF: 248 nm, pulse duration 20 ns) can be irradiated, and the surface contamination can be removed. Thereby, the surface state can always be recovered to a clean state, and the generation efficiency of photoelectrons can always be recovered to a constant state.

  The laser used for the optical cleaning is preferably a short pulse and a short wavelength because the depth of penetration is shallower and the thermal load is small, so that uniform cleaning can be performed, and an excimer laser or the like is preferable.

  1 and 2, even when the EUV exposure is not performed, the surface state is always maintained by performing light cleaning with the laser beam on the photoelectron detection thin film 3. It is possible to recover to a clean state, and it is possible to always recover photoelectron generation efficiency to a constant state.

  The mirror having the EUV light irradiation amount measuring apparatus as described above is used, for example, as a mirror (particularly the M6 mirror closest to the wafer W) of the EUV exposure apparatus shown in FIG. By knowing the amount, it is possible to estimate the amount of EUV light irradiated onto the wafer W during exposure.

It is a figure which shows the outline | summary of the irradiation amount measuring apparatus which is the 1st Embodiment of this invention, and measures the irradiation light irradiated to the multilayer film mirror which comprises an EUV exposure apparatus. It is a graph which shows the change of the photoelectron electric current measured value (A1, A2) with respect to EUV light irradiation time. It is a figure which shows the outline | summary of the irradiation amount measuring apparatus which is the 2nd Embodiment of this invention, and measures the irradiation light irradiated to the multilayer mirror which comprises an EUV exposure apparatus. It is a figure which shows the outline | summary of the irradiation amount measuring apparatus which is the 3rd Embodiment of this invention, and measures the irradiation light irradiated to the multilayer film mirror which comprises an EUV exposure apparatus. It is a figure which shows the outline | summary of an EUV exposure apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Mirror board | substrate, 2 ... Multilayer film, 3 ... Thin film for photoelectron detection, 4 ... Effective area | region, 5 ... EUV light incident range, 6 ... Movable shielding board, 7 ... EUV light, 8 ... Member

Claims (8)

An irradiation light amount measuring apparatus for measuring an irradiation light amount on an irradiated surface of EUV light, provided with a photoelectron current generated by EUV light that irradiates an effective region of the irradiated surface and outside the effective region of the irradiated surface An irradiation light quantity measuring apparatus that measures a photoelectron current generated by EUV light incident on a photoelectron detection thin film and measures an irradiation light quantity based on the measured values of both. 2. The irradiation according to claim 1, wherein a shielding member that shields EUV light is provided so as to be movable between a position that blocks the irradiation of the EUV light to the thin film for photoelectron detection and a position that does not block the EUV light. Light quantity measuring device. 3. The irradiation light amount measuring apparatus according to claim 1, further comprising a light cleaning light source for optically cleaning the surface of the thin film for photoelectron detection. An irradiation light amount measuring apparatus for measuring an irradiation light amount on an irradiated surface of EUV light, wherein the photoelectric current generated by the EUV light irradiating an effective area of the irradiated surface is inserted outside the effective area of the irradiated surface. An irradiation light quantity measuring apparatus that measures a photoelectron current generated by EUV light incident on a photoelectron detection thin film provided in a removable manner, and measures the irradiation light quantity based on both measured values. The irradiation light quantity measuring apparatus according to any one of claims 1 to 4, wherein the photoelectron detection thin film is made of a noble metal. The photoelectron detection thin film made of the noble metal is formed on a glass substrate, and the thin film made of Cr or Ti is formed between the photoelectron detection thin film made of the noble metal and the glass substrate. The irradiation light quantity measuring apparatus according to claim 5. 5. The irradiation light amount measuring apparatus according to claim 1, wherein the photoelectron detection thin film is made of Ni. An EUV exposure apparatus comprising the irradiation light amount measuring apparatus according to claim 1.

Images